Electrical supply and filter system



Jan. 6, 319310 B. F. MIESSNER ELECTRICAL SUPPLY AND FILTER SYSTEM Filed Aug. 23. 1928 Patented Jan. 6, 1931 UNITED STATES PATENT; OFFICE 'BENJAMIN F. mmssnnn, or snow: HILLS, NEW JERSEY, ASSIGNOB, BY MES-NE As- SIGNMENTS, TO RADIO CORPORATION OF AMERICA, OF NEW YORK, N. Y., A COR- PORA'IION OF DELAWARE ELECTRICAL SUPPLY AND FILTER SYSTEM Application filed au ust as, 1928. Serial a. screen.-

The present invention relates generally to electrical supply and filter systems and particularly to such systems in uses requiring a high order of filtration.

A particular object of the invention is to secure-a high order of filtration in association with a source of supply of fluctuating electrical current in which the fluctuating characteristics are more or less severe, and

to do this without excessive use of filter ma-' A. specific object is the economical avoidance of hum production in connection with radio receivers, electrical reproducing phonographs and like devices used for entertainment purposes in which hum from the (men gizing currents would be particularly objectionable.

The current practice in the production of radio broadcast receivers, electrical phonograph reproducers, and like devices, is to energize the three-electrode amplifying tubes from commercially available low cyclage alternating current sources, the unidirectional current required for energizing the plate electrodes oi the tubes being derived through rectiiying the raw alternating current and filtering the rectified components before application to the plate electrodes of tubes. The rectification leaves a uni-directional current rich in fluctuations, thus calling for substantial smoothing out before the current is at all satisfactory in characteristics for employment in connection with amplifying devices, particularly in amplifying devices employing couplings therebetween capable of efficiently tranferring the usual low frequencies oi commercial alternating current. The general practice is to employ filter circuits made up of inductance elements and capacity elements of large values to eilectively smooth out the low frequency ripples involved. These elements are usually weighty, bulky and ex pensive. Arrangements for reducing hum in such devices which also permit of reducing the amount of filter material are of great importance, and my presentinvention is directed particularly to this end.

The invention will be more fully understood by an analysis and description of it in referring to the figures of the accompanying drawing, in which Fig. 1 illustrates the invention in its fun damental aspects and Fig. 2 illustrates the invention employed in connection .with a more or less standard type of radio receiver. Like reference characters represent like parts so far as possible in the two figures.

Fig. 1 conventionally illustrates at S a source of periodically fluctuating uni-directional current. It may be, for example, a direct current generator producing troublesome commutator ripple, or the output of either a single Wave or full Wave rectifier of alternating current, which latter arrangement is the more common one in practice.

The source S feeds the fluctuating current to a filter circuit A comprising a condenser C of low impedance to the fluctuating components and an inductance L of high imped ance to the fluctuating components, this in accordance with well known principles and established practice. There is shown av circuit B which may he ed a work circuit, including some form or cad impedance 1' introduced by the device energized by the current. For example, the load impedance may be the filament-to-plate impedance of a three elect-rode vacuum tube being energized for operation by the source of current.

The work circuit B is shown coupledelectrostatically to the filter circuit A by the condenser G a feature usual to such systems, and the impedance of this condenser to the fluctuating component of the current is usual ly made low by having large capacity. The work circuit is shown to include an inductance coil L and it is one feature of my invention that I couple this coil to coil Lin the filter circuit with such polarity that the litil electromagnetic transfer of energy of the fluctuating component is opposed to the electrostatic transfer of energy of the fluctuating component due to condenser C With this arrangement I have been able to substantial- 1y completely neutralize in work circuit B the ripple effect in the source of supply of unidirectional current, or to produce any de-' sired degree of neutralizing as may be required in apractical system, so that the device being operated by the systemwhich introduces load impedance I is subjected to substantially no fluctuations or any desired degree of fluctuations.

Practice heretofore has depended upon the magnitude of the inductance of coils, such.

as L and L and capacity of condensers, such as C and C for smoothing out the rip ples of the order ofand 120 cycles per second obtained by rectifying the usual commercial 60 cycle source of supply current, the physical proportions and expense of the coils and condensers must be great in order to obtain any results of practical. value, particularly when employing such a system for energizing three-electrode vacuum tubes where the factor of amplification enters into the system and imposes the necessity for a high order of filtration.

It is obvious that in the case of my invention'I do not rely merely on the impedance effects of the elements, but include an ef fective arrangement for neutralizing the fluctuating component in the supply current so that I can employ lesser values of capacity in-the condensers and inductance in the coils, and as a practical matter the differences in these values are most substantial.

Fig. 2 shows an arrangement in which three electrode vacuum'tube VT indicates the usual one or more stages of radio frequency amplification in a radio receiver, the tunable circuit 1 being supplied from a suit able source of radio frequency current energy conventionally indicated by the element K. Tube VT indicates the usual three electrode vacuum tube acting as a detector in such a system supplied fromthe radio frequency portion through thetunable circuit 2, the

arrangement G representing the usual grid leak-stopping condenser combination used in connection with a detector tube.

Tubes V'l and VT; indicate theusual two stages of audio frequency amplification common to such systems having coupling transformers A between the detector stage and the first audio stage and Ag between the first audio stage and the second audio stage. A'translating device LS, indicated as a loud speaken'is shown coupled to the output of tube VT with the aid of a choke coil L and condenser G a couplingarrangement common in practice, but which may be substituted by atWO-Windi'n'g output transformer or any one of the alternative arrangements of practice.' Y

The filaments of tubes VT VT and VT are indicated as energized by raw alternating current through a step-down transformer T as is common in practice, but any other means of energizing may be employed, this feature not being apart of my present invention. The filament of tube VT. is shown as independently energized by raw alternating current through a transformer T this being merely indicative of the usual practice of employing a more powerful tube in the output stage requiring a different degree of energizing than preceding tubes. The grids of the tubes are shown connected to their respective filament systems through. substantially mid-point connections to potentiometers P P and P a common arrangement requiring no detailed explanation.-

A resistance R; is shown connected in the; filament return lead of the radio frequency, amplifier VT and the first audio frequency-- amplifier VT to provide for a grid biasingv potential of particular value for these tubes.

Another resistance R is shown connected in.

the filament return lead of tube VT for obtaining the grid bias potential of this tube, an independent arrangement being shown to indicate the usual practice required because of the use of a more powerfultube in the last splage. In the case of the detector tube VT, t e

detector. For energizing cated a source S of periodically fluctuating The plate electrode of the output tube is shown connected to the positive side of the filter through the choke coil L which choke" coil is indicated as coupled to inductance" Thus in this case" the work circuit includes the choke coil-,L

coil L in the filter circuit.

having condenser C and loud speaker connected in shunt, and this shunt combi nation having the impedance of tube VT in This work circuit is therefore cou-.' pled to the filter circuit electrostatically by series.

means of condenser G and electromagnetically by means of the coupling between'the coils L and L It is particularly desirable to substantially reduce or eliminate the rip"- ples across the shunt connection of coil 1 with condenser C3 and loud speaker LS, and, by properly adjusting the values of cone, denser C and coupling between coils Land. L together with introducing the correct.

grid is shown connected directly to the: filament system to indicate the general practice of not using anysubstantial grid bias.- ing potential for a tube functioning as a.

the plate electrodes of the; several tubes there is conventionally indie.

polarity, the reduction in ripple can be carried out to any desired degree.

It may not be desirable to completely eliminate the ripple in the output of the tube VT because a residual ripple at this part of the system may be usefully employed to oppose fluctuations coming from preceding tubes by Way of audio frequency transformers A, and A In other words instead of trying to adjust the connections to each tube so as to eliminate entirely the ripples in the output circuits of these tubes, an approximate adjustment may be had in them so that the fluctuations arising in preceding tubes are finally neutralized by residual fluctuations in the last tube to give a sort of clean-up effect. The phase of the fluctuations coming from the preceding tubes may be controlled by connecting the transformers A and A, for any desired polarities of transfer. Residual fluctuations arising in the preceding tubes are subject to amplification, so that a small fluctuation in detector tube VT, may be most substantial upon arriving in the plate circuit of tube VT This situation can be nicely handled in several ways. For example, the filtration and neutralizing of the ripple in the preceding stages can be carried out to a greater extent than in the succeeding stages; or if the filtration and neutralizing in the preceding-stages is not carried out to great degree, then the amount of ripple in the succeeding stages can be left lar er than would be ordinarily permissible for ade .quate neutralizing effect. Under such circumstances it may even be desirable to connect coils L and L to have such polarity ofenergy transfer of the fluctuating component as to aid the electrostatic transfer by way of condenser C thereby creating a very large ripple in the output circuit of tube VT, for neutralizing amplified ripple coming from preceding stages.

Radio frequency tube VT and the first audio frequency tube VT are shown con nected to the positive terminal a by way of inductance coil L and potential reducing resistance R it being usual to operate this group of tubes under the same conditions and at lesser potential than the output tube. The inductance coil L in this work circuit is indicated as coupled to filter coil L, and for the same purposes as pointed out in connection with coil L for tube VT However, in some systems it may not be necessary to use a coil L as there is the possibility of relying upon disposing of large fluctuations in preceding tubes by the stage-to-stage bucking previously pointed out. There is shown a condenser connected across the low potential extremity of resistance R, and the negative side of the filter, which condenser is at least of such capacity as to freely by-pass signaling currents handled in the radio frequency and first audio frequency stage.

However, this condenser may be chosen of somewhat lar or value to aid in filtering the current supplied to the plates of these tubes, this depending upon how much efl'ect is given to filtering and neutralizing in the manners previously pointed out.

The potential for energizing'the-plate o detector tube VT is shown obtained by a connection from positive terminal a through potential reducing resistance R In this case, I have not shown an inductance coil coupled to the filter coil L, but in some designs a coil in the detector circuit so coupled may be found of value. I have shown a condenser C connected between the low potential side of resistance R, and the negative side of the filter circuit, this for by-passing si nal currents, and which also may have suitable value for having some desirable effect on the degree of filtration, this, as before pointed out, depending upon the extent to which filtration and neutralizing elsewhere are relied upon.

No limitations are intended by reason of having chosen specific arrangements for illustrative and descriptive purposes, the invention being'one of broad application for many uses apparent to those skilled in the art.

Having thus described my invention, I claim:

1. An electrical system including a'threeelectrode vacuum tube having an output circuit, a filter circuit, and a source of periodically fluctuating uni-directional current for energizing the anode of said tube by way of said output circuit through said filter circuit, said filter being coupled to said output circuit electromagnetically and electrostatically in opposing phase with respect to the fluctuating component of said current energy.

2. An electrical system including a threeelectrode vacuum tube having an output circuit including an inductance element, a filter circuit including an inductance element, a source of periodically'fluctuating uni-directional current for energizing the anode of said tube by way of said output circuit through said filter circuit, and a condenser coupling said filter and output circuits, said inductance elements being electromagnetically coupled together and poled to transfer fluctuating energy in phase opposed to fluctuating 'energy transferred between said filter circuit and said output circuit by said condenser.

3. An electrical system including a plurality of three electrode vacuum tubes having output circuits, afilter circuit, and a source of periodically fluctuating uni-directional current for energizing the anodes of said tubes by way of said output circuits through said filter circuit, said filter circuit being coupled to said output circuits electrostatically, and coupled electromagnetical- 1y to one or more of said circuits in phase to oppose fluctuating energy transferred electrostatically.

4. An electrical system including a plurality of three electrode vacuum tubes connected for audio frequency cascade amplification, a source of uni-directional current periodically fluctuating at audio frequency for energizing the anodes of said tubes, a filter circuit for said current including an inductance coil, and connections between said filter circuit and said tube anodes, the connection to the anode of the last tube of said system including an inductance coil coupled to the inductance coil in said filter circuit with such polarity and degree of coupling as to fix the fluctuations in the output circuit of said last tube in magnitude to substantially neutralize energizing current fluctuations coming from the plate circuits of receding tubes by way'of said cascade ampli cation arrangement.

5. An electrical system including a plurality of three electrode vacuum tubes connected for audio frequency cascade amplification, a source of uni-directional current eriodically fluctuating at audio frequency or energizing the anodes of said tubes, a filter a source of flpctuating unidirectional current energy, a work circuit connected to said source by means comprising lumped series and shunt impedance elements, one of said shunt elements being a condenser having a In testimony whereof I hereunto afiix mysignature.

BENJAMIN F. MIESSNER.

circuit for said current including an inducv tance coil, a connection from the output of said filter circuit to the anode of said last tube including an inductance-coil coupled to the inductance coil of said filter circuit, connections from the output of said filter circuit to the anodes of preceding tubes including potential reducing means, and additional filter means associated with said last-named connections for further filtering the currents supplied to the anodes of saidpreoedin tubes,'the coupling between the coils in sai filter circuit and the output circuit of said last tube being so adjusted as to produce fluctuations of magnitude to substantially neutralize energizing current fluctuations comin from the plate circuits of preceding tubes by way of said cascade amplification arrangement.

6. In an electrical system, the combination of a source of fluctuating unidirectional current energy, a filter circuit for said source including an output condenser having substantial impedance to the fluctuating energy of said source, whereby the fluctuating component of the potential developed across said condenser is a substantial part of the aggregate potential across said condenser, a work circuit connected across said output condenser and means for electromagnetically coupling said Work circuit to said filter circuit of a phase to oppose the fluctuations of the energy of said source whereby the resultant energy flowing in said work circuit is substantially free of any fluctuating component developed therein by said source.

7. In an electrical system, in combination 

